Magnetic materials



United State P iTQ I MAGNETIC MATERIALS 7 John A. James, New Boston, England, assignor to The British Thomson-Houston Company Limited, a British company No Drawing. Application September 1, 1953, Serial No. 377,978 y Claims priority, application GreatBritain September 15, 1952 Claims. (Cl. 204-12) This invention relates to magnetic materials and more particularly to sheet materials of low coercivity suitable for the laminated cores of transformers, motors and generators.

In a paper reported in the Proceedings of the Faraday Society (1936) Finch and Sun described an electrolytic method of forming a sheet of iron in which the majority of the crystals were aligned so as to have at least one cube-edge direction in or nearly in the plane of the sheet. Their process involved the initial production of a thin sheet, or substrate, of a non-magnetic metal, such as gold, silver, the crystals of which were caused to have an orientation similar to that required of the magnetic material subsequently to be produced. The substrate was then mounted on a base, e. g. of stainless steel, from which it could afterwards be removed, and the base with its attached substrate was then subjected to an electrolytic process in a bath of suitable electrolyte whereby a deposit of the desired magnetic material was formed on the substrate. It was discovered that the electrolytically deposited metal acquired (by a process termed epitaxy) a crystal orientation related to that initially imposed on the substrate, so that a desired crystal orientation was thus obtainable. After the substrate with its adherent film of electrolytically deposited magnetic material was detached from the base, the substrate could be removed by chemical action leaving the film alone. Sun and Finch thus produced thin films (having a thickness of the order of .0001") of iron using an electrolyte of ferrous ammonium sulphate having a strength of 350 gr. per litre at a temperature of 20 C., the current density being of the order of 1 amp./dm. They reported, however, that if the thickness of the film was increased beyond 8 x10 the desired crystal structure was lost, so that their process was only of scientific interest. Furthermore, they found that on the removal of the substrate, the orientation was ost.

The object of this invention is to provide an improved method of electrolytically producing sheets of magnetic material in which the majority of the crystals are aligned so as to have two cube edges (100) directions parallel or nearly parallel to two directions at right angles in the plane of the sheet and thus secure further improved magnetic properties.

A process of producing a sheet of iron according to the present invention, consists in preparing a sheet of substrate material having a desired grain-orientation, electrolytically depositing iron on the substrate using an electrolyte offerrous chloride at a temperature of not less than 50 C. and a current density of approximately 1 amp/elm. until a coating of at least .002" has been ob-- tained, and separating the coating from the substrate.

A process of producing sheets of iron according to a further feature of this invention consists in preparing a sheet of substrate material having desired grain orientation, coating the grain-oriented substrate with a layer of a second metal having a related orientation, electrolytically depositing iron on the coated substrate using an electrolyte of ferrous chloride at a temperature of not less than 50 C. with a current density of approximately 1 ampJdm. until a film of at least .002 has been obtained, removing the coated substrate with the deposited film from the electrolyte and stripping the film-from the substrate by removal of the coating.

A preferred base for the purpose of the invention is gold, in which cube texture may be developed by, for example, cold-rolling to or more reduction, and annealing at 1000 C. for 1 hour; The cube-edge length, an, of gold is within 1% 'of /2 times of iron, so that the pattern of atoms in a cube face of an'iron crystal will fit very closely on that of 'atoms in a cube face-of a gold crystal, but with the cube edge directions at 45 to those of the substrate material. Alternatively, copper, iron or a 50/50 nickel-iron alloy can be used as the substrate material.

To form an epitaxial iron electrodeposit on gold we have found that a satisfactory composition of the plating bath is 600 grams FeClzAHzO per litre of water, at an acidity of pH 1.8, and temperature 70 C. It is desirable to limit the evaporation and oxidation of the solution. The cathode current density should be kept small, say 1 A./dm.

In this manner a sheet of iron with the desired magnetic properties is obtained and can be used, in accordance with a further feature of the invention, as a master from which further easily separable sheets can be obtained.

To obtain further sheets the master sheet is covered by electrodeposition with a thin epitaxial layer of a metal with a suitable lattice constant, such as silver or tin, after which the iron deposition is made. The iron sheet can then be parted from the master sheet by removing the intermediate metal by melting or other means.

Tin is a preferred metal because it is cheap and melts at a low temperature. It is suitable because the edge length, a0, of the square face of the tetragonal unit cell of white tin is within 2% of twice the cube edge length of iron.

A suitable composition of the tin plating solution is 90 g. Na2SnOs.3H2O; 7.5 g. NaOH; to 1000 g. water. The cathode current density should be kept small at about 0.1 A./dm. -Tin anodes are used, the solution stirred and the temperature maintained at about 70 C. it is again desirable to limit the evaporation. The tin coating may be as thin as 10- cm., which requires a plating time of about an hour.

Iron may then be deposited on to the tin using the technique described previously and in this way a considerable thickness of deposit can be obtained. With a current density of 1 A./dm. a thickness of 0.005 inch is obtained in approximately 8 hours. This iron deposit may be parted from the master either cold or at a temperature at which the tin is fluid. The iron sheet can be detinned if required by exposing the sheet at room temperature to gaseous chlorine for ten minutes.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A process of producing sheets of iron in which the majority of crystals are aligned to have two cube edges (100) directions substantially at right angles in the plane of the sheets comprising the steps of forming a sheet of substrate material having said grain orientation, electrolytically depositing on the grain oriented substrate a coat ing of a second metal which is removable having a related orientation, electrolytically depositing iron on said coated substrate using an electrolyte of approximately 600 gms. of ferrous chloride, per litre of water and a pH of approximately 1.8 at a temperature of not less than 50 C.

3 with a current density of approximately 1 amp./dm. until a film of at least .002" has been obtained, removing the coated substrate withthe deposited film from the electrolyte and stripping the film from the substrate by removal of the intermediatecoating. V w

2. A process ofrproducingsheets of iron ofa desired grain-orientation which comprises forming a mastersh eet of iron by the process of claim 1 and then repeating the process of said claim using the master sheet so-obtained as the substrate material.

3 A process of producing asheet of iron as defined in claim 1 in which the removable metal used to coat the grain oriented substrate is selected from the group consisting of silver and tin.

4. A process of producing a sheet of iron as defined in claim '1 in "whichthe emovable mtaliised to coat the grain b'riente'd s'iib'sffate'istin. H 4

"5. A process 'of'prodiicifig a 'slit of iron as defined in claim 1 in which the removable metal used to coat the grain oriented substrate is silver.

References Cited in the file of this patent UNITED STATES PATENTS 992,951 Fischer May 23, 1911 992,952 Fischer -Q May 23, 1911 2,165,027 Bitter July 4, 1939 2,706,329 Hcspenheide Apr. 19, 1955 OTHER REFERENCES Finch and Sun: Trans. of the Fa'r'a'day Society, vol. 32, 1936, pp. 852-863. p I

Zeitschrift'fiir Elecktr'oc'he'r'nie, Vol.47, 1941, 'pp. 135- Journal of Science of Hiroshima University, Japan, vol. 11, 1942, PP- 89-92. 

1. A PROCESS OF PRODUCING SHEETS OF IRON IN WHICH MAJORITY OF CRYSTALS ARE ALIGNED TO HAVE TWO CUBE EDGES (100) DIRECTIONS SUBSTABTIALLY AT RIGHT ANGLES IN THE PLANE OF THE SHEETS COMPRISING THE STEPS OF FORMING A SHEET OF SUBSTRATE MATERIAL HAVING SAID GRAIN ORIENTATION, ELECTROLYTICALLY DEPOSITING ON THE GRAIN ORIENTED SUBSTATE A COATING OF A SECOND METAL WHICH IS REMOVABLE HAVING A RELATED ORIENTATION, ELECTROLYTICALLY DEPOSITING IRON ON SAID COATED SUBSTRATE USING AN ELECTROLYTE OF APPROXIMATELY 600 GMS. OF FERROUS CHLORIDE, PER LITRE OF WATER AND A PH OF SPPROXIMATELY 1.8 AT A TEMPERATURE OF NOT LESS THAN 50* C. WITH A CURRENT DENSITY OF APPROXIMATELY 1 AMP./DM.2 UNTIL A FILM OF AT LEAST .002" HAS BEEN OBTAINED, REMOVING THE COATED SUBSTRATE WITH THE DEPOSITED FILM FROM THE ELECTROLYTE AND STRIPPING THE FILM FROM THE SUBSTRATE BY REMOVAL OF THE INTERMEDIATE COATING. 